A surface protection film is used for the purpose of protecting the surface of a prism sheet or the like, which is used for synthetic resin plates or stainless-steel plates used as building materials, aluminum plates, decorative plywood, steel plates, glass plates, furniture, household goods, home appliances, precision machines and automobiles, and also for optical applications, from scratch, dust, and stain.
As an adhesive used for the adhesive layer of such a surface protection film, an acrylic adhesive, and a rubber adhesive mainly comprising rubber such as natural rubber and polyisobutylene, have been conventionally used. As a method of applying such an adhesive to a predetermined supporting film, a method of applying an adhesive solution prepared by dissolving an adhesive in a solvent to the film, using a roll, a spray, etc., has been used. Such a method is advantageous in that an adhesive layer can be uniformly and thinly applied to the supporting film. However, from the viewpoint of air pollution, fire, industrial safety and health upon production, economic efficiency and the like, the use of a solvent is not preferable.
For such a reason, recently, a co-extrusion film formed by integrating a base material layer made of a polyolefinic resin with an adhesive layer comprising a hydrogenated styrene elastomer or olefinic elastomer has been preferably used.
These surface protection films have the following some required characteristics. For example, the surface protection film is required not to cause the floating or peeling thereof easily, when the adherend product thereof is stored or transported. In addition, the surface protection film is also required such that a user can easily peel the film from the adherend with a small power, namely, the tack strength of the adhesive layer is not increased (tackiness is not increased) by factors such as the time and temperature applied to the storing of the surface protection film.
Moreover, the surface protection film is also required not to contaminate the surface of the adherend, namely, a portion of the adhesive layer, or low-molecular-weight compounds such as antioxidants or powders (outer lubricants), which are comprised in the adhesive layer, when the surface protection film peal, do not migrate to the surface of the adherend. This property is particularly important in a case where the adherend is an optical member.
Furthermore, the surface protection film is generally produced and stored in the form of a roll, and it is fed before use. It is also important for the surface protection film that only a small power is needed for this feeding, namely, to have high release property.
For the purpose of satisfying the above described required characteristics, various studies and proposals have been conducted. For example, there has been proposed a surface protection film, which comprises an adhesive layer containing a styrene elastomer and a tackifier, and a base material layer adjacent to the adhesive layer, containing an olefinic elastomer with a specific structure (see, for example, Patent Literature 1).
Moreover, a large number of surface protection films, each of which has an adhesive layer containing a hydrogenated styrene elastomer with a specific structure and a base material layer consisting of a thermoplastic resin, have been proposed (see, for example, Patent Literature 2, 3, and 4).